Problem: Simplify the following expression: $t = \dfrac{6z}{7} - \dfrac{2z}{5}$
Answer: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $7$ and $5$ $\lcm(7, 5) = 35$ $ t = \dfrac{5}{5} \cdot \dfrac{6z}{7} - \dfrac{7}{7} \cdot \dfrac{2z}{5} $ $t = \dfrac{30z}{35} - \dfrac{14z}{35}$ $t = \dfrac{30z -14z}{35}$ $t = \dfrac{16z}{35}$